A new method to quantitate the fit of elastomeric half-mask and full-facepiece air-purifying respirators was developed. In this method the two flows, cartridge flow and leak flow, are separate. The air-purifying cartridges of the respirator are attached to a reference respirator. A selected flow equivalent to the inhalation flow of the wearer is drawn through the cartridge pair: A feedback system consisting of a pressure controller and a control valve is used to set the pressure drop in the mask on the subject's face equal to the pressure drop in the reference mask. The faceseal leak flow is measured while the subject holds his or her breath for a short period of time. The ratio of total flow (cartridge flow+leak flow) to leak flow is a measure of fit and is defined as the flow fit factor. Aerosol fit factors and flow fit factors were determined using sampling probes in three mask locations: top, center, and bottom. A Kruskal-Wallis test showed that aerosol fit factors obtained from the three locations were significantly different from each other (p=0.0001) while the corresponding flow fit factors were not. Aerosol fit factors obtained with the center probe had the least variability. The coefficient of variation in aerosol fit factors ranged from 5.4% for the center probe to 19% for the bottom probe; the coefficient of variation in flow fit factors was much lower, ranging from 1.7% for the top probe to 2.2% for the center and bottom probes.
Krishnan, U., Willeke, K., Juozaitis, A., Lehtimäki, M., & Szewczyk, K. (1994). Development of a dichotomous-flow quantitative fit test for half-mask and full-facepiece respirators. American Industrial Hygiene Association Journal, 55(3), 223-229. https://doi.org/10.1080/15428119491019069